1. Field of the Invention
The present invention relates to an ink set comprising at least two yellow ink compositions different from each other in lightness.
2. Background Art
Ink jet recording is a printing method wherein droplets of an ink composition are ejected and deposited on recording media, such as paper, to perform printing. The feature of the ink jet recording method is that images having a combination of high resolution with high quality can be printed at a high speed by means of a relatively inexpensive apparatus. Ink jet recording apparatuses utilizing this method have been commercially widely accepted by virtue of good print quality, low cost, relatively quiet operation, and capability of forming graphics.
In recent years, a method has been carried out wherein a plurality of color ink compositions are provided and used to form color images by ink jet recording. In general, color images are formed using three colors of a yellow ink composition (Y), a magenta ink composition (M), and a cyan ink composition (C), or optionally four colors of a yellow ink composition (Y), a magenta ink composition (M), a cyan ink composition (C), and a black ink composition (K).
In the recording method using these ink compositions, hue and lightness, which are measures of colors, are regulated by the following method to print images including a wide range of natural colors. Hue, that is, the so-called xe2x80x9ccolorxe2x80x9d such as red or blue, is regulated by varying the ratio of color dots of cyan, magenta, and yellow ejected from an ink head. The lightness, that is, brightness, is regulated by varying the density of dots formed. The regulation of the density of each color dot formed on a recording medium in this way can realize printing of images including a wide range of natural colors.
Further, in recent years, color images have become formed using six colors of the above four color ink compositions and, in addition, a cyan ink composition having low color density (a light cyan ink composition) and a magenta ink composition having low color density (a light magenta ink composition), or using seven colors of the above six colors and a yellow ink composition having low color density (a light yellow ink composition). These ink compositions used for the formation of color images as such should exhibit good color development, and, in addition, these ink compositions, when used in combination with a plurality of ink compositions, should develop good intermediate colors. That is, in the ink compositions and an ink set using these ink compositions, faithful image reproduction and a wide color reproduction range are desired.
The present inventors have now found that the use of two yellow ink compositions different from each other in lightness, that is, the use of a yellow ink composition in combination with a dark yellow ink composition having lower lightness than the yellow ink composition, can realize images having good quality, especially can prevent the occurrence of graininess in recorded images and can significantly broaden the color reproduction range of images. The present invention has been made based on such finding.
Accordingly, it is an object of the present invention to provide an ink set which can realize images having good quality, especially color images with a wide color reproduction range and excellent image reproduction.
According to one aspect of the present invention, there is provided an ink set comprising at least a normal yellow ink composition and a dark yellow ink composition,
the lightness of the dark yellow ink composition being lower than that of the normal yellow ink composition.
According to another aspect of the present invention, there is provided an ink set comprising at least a normal yellow ink composition and a dark yellow ink composition, wherein
for the dark yellow ink composition, the absolute value of b*/a* in the L*a*b* color system as calculated from the spectral characteristics of a 1000-fold dilution of the dark yellow ink composition with water is not less than 0.83, and the b* value is not less than zero (0) and is smaller than the b* value of the normal yellow ink composition as calculated from the spectral characteristics of a 1000-fold dilution of the normal yellow ink composition with water.